The present invention relates to novel improvements in a differential scanning calorimeter, which is one kind of thermal analysis instrument for examining changes in physical properties of a material with temperature or time. More particularly, the invention relates to novel improvements in the detector structure of a heat-flux differential scanning calorimeter.
Differential scanning calorimeters (hereinafter referred to as DSCs) are classified into power-consumption DSC and heat-flux DSC according to the method of detecting heat flux. In the power-consumption DSC, a sample holder and a reference holder have respective heaters. The heat fluxes to the sample and to the reference substance are controlled by energization of the heaters. The heat flow is detected from the electric power difference. On the other hand, the heat-flux DSC has a heat sink having relatively large heat capacity. A heat conductor is mounted between the heat sink and the sample holder. Another heat conductor is mounted between the heat sink and the reference holder. Heat flow due to heat exchange is detected as a temperature difference. Generally, the power-consumption DSC has a feature of good heating and cooling response because the sample holders have small heat capacity and are directly heated. On the other hand, heat-flux DSC has a feature of good baseline stability because it has a heat sink (for example, see T. Hatakeyama and F. X. Quinn xe2x80x9cThermal analysis, Fundamentals and Applications to Polymer Sciencexe2x80x9d, John Wiley (1994)xe2x80x9d. A detector structure for the heat-flux differential scanning calorimeter having such features is described by T. Hatakeyama and F. X. Quinn, xe2x80x9cThermal analysis, Fundamentals and Applications to Polymer Sciencexe2x80x9d, John Wiley (1994), p. 9, and is constructed as follows.
a) A sample holder and a reference holder are placed on a heat-sensitive disk. The circumference of the disk is coupled to a heat sink and heat exchange is made. The temperature difference is measured at the rear surfaces of the holders.
b) A sample holder and a reference holder are placed at symmetrical positions on the same plane within a heat sink. Heat conductors are mounted between the bottom surface of the heat sink and the holders, respectively. Heat exchange is made. The temperature difference is measured at given positions on the heat conductors.
c) According to a catalog of FP85 (double-decker DSC) of Metler Corporation (Switzerland), two disklike heat conductors are coupled to a cylindrical heat sink in a vertically spaced relation to each other. A sample holder is placed in an upper position, while a reference holder is placed in a lower position. The temperature difference is measured across the rear surfaces of the holders.
The heat-flux DSC is characterized in that the baseline is stable because a heat sink having a large heat capacity is used. However, the large heat capacity deteriorates the heating and cooling response of the heat sink.
A heater is generally wound around the cylindrical heat sink to control the temperature. In order to reduce the heat capacity of the heat sink for improving the heating and cooling response, the diameter of the heat sink is reduced, the height of the cylindrical heat sink is decreased, the thickness of the wall of the heat sink is decreased, the heat sink is made from a material having a small specific heat capacity, or other method is employed.
Silver or copper having good thermal conductivity is often used as the material to provide uniform temperature distribution except in special cases. An appropriate wall thickness is substantially determined by taking account of the mechanical strength and to mitigate pulsation of the heater control. Decreasing the height and the diameter contributes directly to a decrease in the heat capacity. Decreasing the diameter contributes more.
In the DSC where the sample holder and the reference holder are mounted on the same plane as in the prior art techniques a) and b), limitations are imposed on diameter decrease, although this decrease contributes most to decrease in the heat capacity of the heat sink in improving the heating and cooling response. That is, the diameter of the heat sink needs to be at least twice as large as the diameter of the sample container. Where the temperature distribution on the circumference of the heat sink is taken into consideration, it is desired to place the sample holder and the reference holder at symmetrical positions at the closest possible position to the center on the same plane to stabilize the baseline. Hence, it is not desirable to decrease the diameter very much from this point of view. In other words, it is difficult to decrease the heat capacity of the heat sink to improve the heating and cooling response while securing stability of the baseline.
In the structure where the holders are disposed with the two stages of disks as in the prior art technique c), the sample holder can be placed in the center of the circumference of the heat sink. Furthermore, the diameter of the heat sink can be reduced even to near the diameter of the sample container. In this structure, however, the entrance port for the heat flow from the heat sink to the sample holder is spaced in the vertical direction of the cylinder from the entrance port for the heat flow from the heat sink to the reference holder. It is difficult to stabilize the baseline by the effects of the temperature distribution in the vertical direction.
To solve the foregoing problem, the present invention provides a differential scanning calorimeter comprising, a sample holder on which a sample container is disposed, a reference holder provided symmetrically with respect to a certain plane which is parallel to a sample-disposed plane of the sample holder, a heat sink surrounding both holders, the heat sink being in the shape of a rotation symmetry body having a rotation axis perpendicular to the certain plane, heat conductors coupled to the inner surface of the heat sink crossed by the certain plane and coupled to the ends of both holders so as to make heat exchange between the heat sink and the holders, and temperature detectors coupled to each opposite surface of both holders.
In the heat flow detection mechanism of the structure described above, the entrance port for heat flow going from the heat sink to the sample holder is the same as the entrance port for heat flow going from the heat sink to the reference holder. Therefore, a baseline having good stability can be obtained without being affected by the vertical temperature distribution in the heat sink. Furthermore, the inside diameter of the heat sink can be decreased to near the diameter of the sample container. Note that decreasing the inside diameter of the heat sink contributes most to decrease in the heat capacity of the heat sink in improving the heating and cooling response to the heat sink. The heating and cooling response can be improved dramatically while securing stability of the baseline of the heat-flux DSC.